Intensity modulated fiber optic pressure sensor

Abstract

A fiber optic pressure sensor featuring a cartridge housing having an end that is exposed to the atmosphere, a thin flexible membrane covering the exposed end of the cartridge housing such that the flexible membrane has an exposed side and a protected side. A fiber bundle is disposed within the cartridge housing, featuring a transmitting fiber having a first and second ends. The first end has a polished finish and the second end is coupled to a light source. The fiber bundle also features a multitude of receiving fibers disposed around the transmitting fiber with each receiving fiber having first and second ends where the first ends are also polished. The fiber bundle is disposed within the cartridge housing such that the first end of the transmitting fiber and the first end of each receiving fiber is adjacent to the protected side of the flexible membrane with free space between the first fiber end and the protected side of the flexible membrane. A light sensing means is coupled to second end of said receiving fibers wherein light launched into the transmitting fiber propagates emerges at the polished end, propagates a very short distance in air, and is reflected by the flexible membrane into the receiving fibers, propagates therethrough, and is detected by light sensing means. Upon a change in the atmospheric pressure, pressure waves cause the flexible membrane to distort causing a change in the amount of light reflected by the protected side of the flexible membrane. Thus the intensity of the light coupled into the sensing fibers begins to modulate in relation to the intensity of pressure wave.

1. A fiber optic pressure sensor comprising:
 a cartridge housing having an end that is exposed to the atmosphere; 
 a thin flexible membrane covering the exposed end of the cartridge housing such that the flexible membrane has an exposed side and a protected side; 
 a fiber bundle disposed within the cartridge housing, the fiber bundle comprising
 a transmitting fiber having a first and second end, the first end having a polished finish and the second end coupled to a light source, and 
 a multitude of receiving fibers disposed around the transmitting fiber, each receiving fiber having first and second ends, 
 
 the housing end extending beyond the first end of the transmitting fiber and the first ends of the receiving fibers in a direction along a fiber axis to maintain the membrane at a distance from the fibers, 
 the fiber bundle is disposed within the cartridge housing such that the first end of the transmitting fiber and the first end of each receiving fiber is adjacent to the protected side of the flexible membrane with free space between the first fiber end and the protected side of the flexible membrane; and 
 light sensing means coupled to second end of said receiving fibers, 
 wherein light launched into the transmitting fiber emerges at the polished end, propagates a very short distance in air, and is reflected by the flexible membrane into the receiving fibers, propagates therethrough and is detected by the light sensing means, upon a change in the atmospheric pressure, pressure waves cause the flexible membrane to distort causing the amount of light reflected by the protected side of the flexible membrane and the intensity of the light coupled into the receiving fibers to modulate. 
 
   
   
     2. The fiber optic pressure sensor of  claim 1  wherein the cartridge housing is constructed of a rigid and light weight material. 
   
   
     3. The fiber optic pressure sensor of  claim 1  wherein the cartridge housing comprises means to adjust the distance between the polished end of the transmitting fiber and the flexible membrane. 
   
   
     4. The fiber optic pressure sensor of  claim 1  wherein the cartridge housing comprises means to adjust the tension of the flexible membrane drawn across the exposed end of the cartridge housing. 
   
   
     5. The fiber optic pressure sensor of  claim 1  wherein the flexible membrane comprises a coating on the protected side to enhance its light reflecting properties. 
   
   
     6. The fiber optic pressure sensor of  claim 5  wherein the flexible membrane comprises mylar with at least one surface coated with thin aluminum film. 
   
   
     7. The fiber optic pressure sensor of  claim 1  wherein the fiber bundle comprises a single multimode transmitting fiber and a multitude of receiving fibers all encased in a protective tubing, the tubing disposed within the cartridge housing. 
   
   
     8. The device of  claim 7  wherein the protective tubing is a stainless steel tubing. 
   
   
     9. The device of  claim 1  wherein the light sensing means is at least one silicon PIN diode. 
   
   
     10. The device of  claim 1  wherein the light source is a light emitting diode. 
   
   
     11. A fiber optic pressure sensor comprising:
 a cartridge housing having an end that is exposed to the atmosphere; 
 a thin flexible membrane covering the exposed end of the cartridge housing such that the flexible membrane has an exposed side and a protected side; 
 a fiber bundle disposed within the cartridge housing, the fiber bundle comprising
 a transmitting fiber having a first and second end the first end having a polished finish and the second end coupled to a light source, and 
 a receiving fiber having a first and a second end, disposed adjacent to the transmitting fiber, 
 
 the fiber bundle is disposed within the cartridge housing such that the first end of the transmitting fiber and the first end of the receiving fiber is adjacent to the protected side of the flexible membrane with free space between the first fiber end and the protected side of the flexible membrane, 
 the housing end extending beyond the first end of the transmitting fiber and the first end of the receiving fiber in a direction along a fiber axis to maintain the membrane at a distance from the fibers; and 
 light sensing means coupled to the second end of said receiving fiber, 
 wherein light launched into the transmitting fiber emerges at the polished end, propagates a very short distance in air, and is reflected by the flexible membrane into the receiving fiber, propagates therethrough and is detected by light sensing means, upon a change in the atmospheric pressure, pressure waves cause the flexible membrane to distort causing the amount of light reflected by the protected side of the flexible membrane and the intensity of the light coupled into the receiving fiber to modulate. 
 
   
   
     12. The fiber optic pressure sensor of  claim 11  wherein the cartridge housing is constructed of a rigid and light weight material. 
   
   
     13. The fiber optic pressure sensor of  claim 11  wherein the cartridge housing comprises means to adjust the distance between the polished end of the transmitting fiber and the flexible membrane. 
   
   
     14. The fiber optic pressure sensor of  claim 11  wherein the cartridge housing comprises means to adjust the tension of the flexible membrane drawn across the exposed end of the cartridge housing. 
   
   
     15. The fiber optic pressure sensor of  claim 11  wherein the flexible membrane comprises a coating on the protected side to enhance its light reflecting properties. 
   
   
     16. The fiber optic pressure sensor of  claim 15  wherein the flexible membrane comprises mylar with at least one surface coated with thin aluminum film. 
   
   
     17. The fiber optic pressure sensor of  claim 11  wherein the fiber bundle comprises a multimode transmitting fiber and a multimode receiving fiber encased in a protective tubing. 
   
   
     18. The device of  claim 17  wherein the protective tubing comprises stainless steel tubing. 
   
   
     19. The device of  claim 11  wherein the light sensing means is at least one silicon PIN diode. 
   
   
     20. The device of  claim 11  wherein the light source is a light emitting diode. 
   
   
     21. A fiber optic pressure sensor comprising:
 a cartridge housing having an end that is exposed to the atmosphere, 
 a thin flexible membrane covering the exposed end of the cartridge housing such that the flexible membrane has an exposed side and a protected side; 
 a fiber bundle disposed within the cartridge housing, the fiber bundle comprising a single transmitting and receiving fiber having a first and second end, the first end having a polished finish and the second end couple to a light source, 
 the housing end extending beyond the first end of the fiber in a direction along a fiber axis to maintain the membrane at a distance from the fibers, 
 the fiber bundle is disposed within the cartridge housing such that the first end of the fiber is adjacent to the protected side of the flexible membrane with free space between the first fiber end and the protected side of the flexible membrane; 
 light sensing means also coupled to second end of said fiber, 
 wherein light launched into the fiber propagates through the fiber, emerges at the polished end, propagates a very short distance in air, and is reflected by the flexible membrane back into the fiber, propagates therethrough and is detected by light sensing means, upon a change in the atmospheric pressure, pressure waves cause the flexible membrane to distort causing the amount of light reflected by the protected side of the flexible membrane and the intensity of the light coupled into the fiber to modulate. 
 
   
   
     22. A sensor according to  claim 1 , wherein the membrane and the cartridge housing form a space separated from an exterior of the sensor by the membrane and the housing. 
   
   
     23. A sensor according to  claim 22 , wherein the space contains the air. 
   
   
     24. A sensor according to  claim 1 , wherein the receiving fibers are multimode fibers. 
   
   
     25. A sensor according to  claim 11 , wherein the membrane and the cartridge housing form a space separated from an exterior of the sensor by the membrane and the housing. 
   
   
     26. A sensor according to  claim 25 , wherein the space contains the air. 
   
   
     27. A sensor according to  claim 11 , wherein the receiving fiber is a multimode fiber. 
   
   
     28. A fiber optic pressure sensor comprising:
 a cartridge housing having an end that is exposed to the atmosphere; 
 a thin flexible membrane covering the exposed end of the cartridge housing such that the flexible membrane has an exposed side and a protected side; and 
 a fiber bundle disposed within the cartridge housing, the fiber bundle comprising
 a transmitting fiber having a first and second end, the first end having a polished finish, the second end arranged for being coupled to a light source, and 
 a plurality of receiving fibers disposed around the transmitting fiber, each receiving fiber having first and second ends, 
 
 the fiber bundle being disposed within the cartridge housing such that the first end of the transmitting fiber and the first end of each receiving fiber is adjacent to the protected side of the flexible membrane with free space between the first fiber end and the protected side of the flexible membrane, the free space containing a gas, 
 the housing end extending beyond the first end of the transmitting fiber and the first ends of the receiving fibers in a direction along a fiber axis to maintain the membrane at a distance from the fibers. 
 
   
   
     29. The fiber optic pressure sensor according to  claim 28 , wherein the gas is air. 
   
   
     30. The fiber optic pressure sensor according to  claim 28 , wherein light emerges from the polished end of the transmitting fiber and is reflected by the flexible membrane into the receiving fibers, wherein a change in the atmospheric pressure external to the cartridge housing causes the flexible membrane to distort, causing an amount of light reflected by the protected side of the flexible membrane and the intensity of the light coupled into the receiving fibers to modulate. 
   
   
     31. The fiber optic pressure sensor according to  claim 28 , further comprising a light sensor arranged to receive light from the receiving fibers. 
   
   
     32. The fiber optic pressure sensor according to  claim 28 , further comprising a tensioner arranged to adjust the membrane tension. 
   
   
     33. The fiber optic pressure sensor according to  claim 32 , wherein the tensioner includes a threaded body threadingly engaged between the cartridge housing and a draw nut. 
   
   
     34. A fiber optic pressure sensor comprising:
 a cartridge housing having an end that is exposed to the atmosphere; 
 a thin flexible membrane covering the exposed end of the cartridge housing such that the flexible membrane has an exposed side and a protected side; and 
 a fiber bundle disposed within the cartridge housing, the fiber bundle comprising
 a single transmitting fiber having a first polished end and a second end for being coupled to a light source, and 
 a single receiving fiber adjacent to the transmitting fiber, the receiving fiber having first and second end, the second end for being coupled to a light sensing device, 
 
 the fiber bundle being disposed within the cartridge housing such that the first end of the transmitting fiber and the first end of each receiving fiber is adjacent to the protected side of the flexible membrane with free space between the first fiber end and the protected side of the flexible membrane, the free space containing a gas, 
 the housing end extending beyond the first ends of the fibers in a direction along a fiber axis to maintain the membrane at a distance from the fibers. 
 
   
   
     35. The sensor according to  claim 34 , wherein light emerges from the polished end of the transmitting fiber and is reflected by the flexible membrane into the receiving fiber, wherein a change in the atmospheric pressure external to the cartridge housing causes the flexible membrane to distort, causing an amount of light reflected by the protected side of the flexible membrane and the intensity of the light coupled into the receiving fiber to modulate. 
   
   
     36. A fiber optic pressure sensor according to  claim 21 , wherein the fiber is multimode. 
   
   
     37. A fiber optic pressure sensor according to  claim 21 , wherein the fiber is multimode. 
   
   
     38. A fiber optic pressure sensor comprising:
 a cartridge housing having an end that is exposed to an atmosphere, 
 a thin flexible membrane covering the exposed end of the cartridge housing such that the flexible membrane has an exposed side and a protected side, 
 a fiber bundle disposed within the cartridge housing, the fiber bundle including at least one optical fiber, the fiber bundle being disposed within the cartridge housing such that the first end of the transmitting fiber is adjacent to the protected side of the flexible membrane with free space between the first fiber end and the protected side of the flexible membrane, the free space being separated from the atmosphere by the cartridge housing and the membrane and having a gas enclosed therein, 
 and at least one member threadingly engaged with the cartridge housing arranged to adjust the tension of the membrane or a distance between the first fiber end and the membrane. 
 
   
   
     39. The sensor of  claim 28 , the transmitting fiber being arranged at a centerline of the fiber bundle. 
   
   
     40. The sensor of  claim 28 , the sensor membrane being spaced apart from the first ends of the receiving fibers by 180 to 250 microns. 
   
   
     41. The sensor of  claim 28 , wherein the plurality of receiving fibers includes six receiving fibers. 
   
   
     42. The sensor of  claim 28 , wherein sensor has an acoustic sensitivity of at least 1.5×10 −9  W/Pa over a frequency range of 50 to 1000 Hz.